This exploratory/developmental application (R34) requests funds to design and pilot an HIV and substance use prevention program for 16-20 year-old ethnically-diverse, young men who have sex with men (YMSM). We will combine and adapt three innovative HIV and substance use prevention programs originally developed for adult MSM (Project MIX), runaway youth (Street Smart), and mentally ill adolescents (Project BALANCE). Project MIX is a federally-funded behavioral intervention for MSM who use drugs/alcohol. Street Smart is in the CDC compendium of empirically supported HIV prevention programs. Project BALANCE is an ongoing HIV prevention program for teens with psychiatric disorders. In stage 1, we will work with our advisory board and gather information from key young adult HIV+ MSM informants (N=21) to develop a uniquely tailored manualized intervention for YMSM drawing on Project MIX, Street Smart, and Project BALANCE. In stage 2, we will pilot test the intervention with cohort 1 -- a community-based sample of 20 ethnically-diverse YMSM (2 groups of 10 YMSM). We will examine the intervention's feasibility, acceptability and tolerability, and we will evaluate our tracking and retention strategies. We will refine the curriculum and study procedures based on participant feedback and advisory board input. In stage 3, we will test the revised intervention in a pilot randomized controlled trial (RCT) in a sample of 100 YMSM (cohort 2) - 50 YMSM in the experimental group and 50 YMSM in a control group. Cohort 1 will complete baseline and 3-month follow-up assessments to evaluate tracking and retention strategies. Cohort 2 will complete baseline, 3-, and 6-month follow-up to evaluate preliminary treatment effects. The intervention will be informed by social learning theory and a social- personal framework previously applied to the sexual and drug use behavior of at-risk youth. The intervention will target key determinants of risk taking among our specific population of YMSM, including: psychological well- being and emotion regulation, personal attributes, peer and partner relationships, sexual context variables, and sexual minority stress. Data analyses will (a) evaluate change in adolescent risky sexual behavior and substance abuse as a function of program participation, and (b) determine the pretest-posttest effect size of program impact on the outcome variables. We will use the effect size to determine the sample size needed for a more definitive test of the intervention in the future. Our target population, young men who have sex with men age 16-20, is one of the highest U.S. risk groups for HIV/AIDS acquisition, yet one that is woefully under-represented in the intervention literature. Empowered with the right tools, YMSM will be better equipped to make decisions that reduce the spread of HIV. Consistent with R34 guidelines to support the early phase of intervention development and pilot testing, the final product will form the basis for a full-scale intervention trial for YMSM. This study is part of an overall program of research designed to understand and prevent HIV infection among high-risk youth.